Early computer designs generally included a chassis with a plurality of individual components and assemblies mounted therein and connected to one another by means of wires, cables, brackets, nuts, bolts and the like. A major computer design advance occurred with the advent of printed circuit boards, integrated circuits and modular component assemblies. The printed circuit boards were, for example, formed of lightweight material and housed a myriad of components which were electrically interconnected with the component assemblies through wiring harnesses. The wiring harnesses and hard wire connections were subsequently replaced by technologically advanced connectors used for integrally coupling the individual components to each other and to other circuitry in the computer.
In the design of electronic equipment, the use of connectors, modular components, and specialized hardware has permitted key components and printed circuit boards to be efficiently added and removed. Such ease in the addition and deletion of computer components and printed circuit boards has facilitated assembly repair, upgrade, and/or changes in functionality.
Computer reliability and serviceability are also valuable design aspects. Originally, a rule of practice in the maintenance of electrical circuitry, such as computer hardware, was that of always turning the power to the computer off before components or printed circuit boards were added or removed from the computer chassis or support frame. Recent innovations have addressed the desirability to insert and remove modular components and printed cards from electrical equipment, such as computer hardware, when the computer is electrically connected and operational, i.e. "hot." This is now possible for hot plugable hard drives, and in these cases, the power may be disconnected from only the connector of the drive to be inserted and removed while allowing the adjacent components to remain "hot."
Removable computer components today include disc drives, drive cages, fans, power supplies, system I/O modules, processor boards, and other subassemblies. As referenced above, the removability of computer components allows for better overall serviceability of the computer system, which is a distinct advantage to both the user and the maintenance technician. A defective power supply in the main or central computer generally requires prompt replacement in order to limit downtime. It is for this reason that modular components and connectors facilitate prompt replacement and are thus popular in many computer designs.
The modularity of computer systems is thus recognized as an important design consideration. As referenced above, modules can be removed and examined for operability or other purposes much easier than permanently mounted fixtures within a computer chassis. Because computers provide an integral part of most business operations, it is of utmost importance to maintain the reliability and integrity of the computer system. When the various elements of a computer can be easily removed in a modular form, they can also be replaced to maintain the operational status of the computer.
Despite the advantages of allowing electrical components of a computer system to be hot plugable there are certain concerns and potential problems associated with hot plugable computer systems. Frequently, hot plugable computer systems are housed within a computer chassis and rack mounted into a frame on sliding rollers which allow the computer chassis to be pulled out of the rack frame and exposed. When the system is to be serviced, the chassis is pulled from the rack frame and a top cover panel is removed to expose the modules and associated components. The removal of the top cover panel can create various problems. First, the removed panel must be put aside and risks being lost, bent or otherwise damaged. Second, the removal of the top cover panel exposes all the modules and components housed within the computer chassis. In certain situations there may be modules or components which are not hot plugable and are best left covered and protected during a servicing operation. Third, cooling of the modules and components within the computer chassis are increasingly dependent on specifically calculated air flows which are contingent on the presence of the top cover panel. There may be components having cooling needs which require the presence of the top cover panel even during the servicing operation and are therefore, best left covered during the servicing operation. Furthermore, there is a risk that the computer chassis will be slid back into the rack frame without the top cover panel being replaced, especially if the panel was damaged or lost during the servicing operation, thereby preventing proper cooling of the computer system.
It would be advantageous, therefore, to devise a rack mountable computer chassis which allows access to hot plugable modules and components for their servicing while at the same time covering other modules or components which require protection during the servicing operation. It would further be advantageous if such a chassis allowed access to the hot serviceable modules and components while at the same time maintaining the top cover panel as an integral part of the computer chassis during the servicing operation. It would still further be advantageous if such a chassis prevented the chassis from being slid back into a rack frame without the top cover panel being replaced.